1. Field of the Invention
The present invention relates generally to shutter assemblies and more particularly to a photographic-type shutter that relies on electromagnetic forces to open and close and which is, in one embodiment, self-damping to reduce impact and rebound when the shutter is opened or closed.
2. Description of Related Art
Electrically operated lens shutters used in various types of photographic and laboratory equipment are well known in the art. Lens shutters especially adapted for high speed opening and closing can operate in fractions of a second. An open/close cycle can take place in 30-40 milliseconds or less and repeated cycles at frequencies of 30 cycles per second are common.
Lens shutters generally are of two types. In one type, a so-called “guillotine” shutter has one or two thin, metal blades or leaves arranged to cover a lens opening. Pivot connections allow each blade to swing between a closed position where the blades cover the lens opening and an open position where the blades are drawn aside from the lens opening.
In a second type of shutter a plurality of pivotally mounted blades, usually five, is arranged around the lens opening. Each blade is connected to a rotatable drive ring. In the operation of these shutters, the rotation of the drive ring in one direction causes the blades to swing in unison to an open position. Counter rotation of the ring swings the blades to a closed position over the lens opening after exposure. Generally a linear electric motor is used to activate the shutter. When activated, the linear motor pulls on a lever arm that rotates the drive ring to open the shutter. To close the shutter the motor is deactivated and a spring causes the counter rotation of the drive ring to close the shutter. As noted above, shutters of this sort can cycle open and close 30 times per second.
It is common in both types of shutters to provide a shock absorber or damper that absorbs the impact as the blades are pivoted between the open and closed positions. In this respect, reference is made to various US patents including U.S. Pat. Nos. 3,595,553; 3,664,251 and 6,652,165 the disclosures of which are incorporated herein by reference. As disclosed in these references, the shock absorber operates to stop the shutter blade very rapidly, yet softly and without damage. There also is little or no bounce as the shutter first is snapped open by the linear electric motor and then is snapped closed by the spring when the motor is deenergized.
In some applications, however, it is desirable to hold the shutter open for an extended period to prolong the exposure time. In these cases it has been the practice to keep the motor activated for the duration of the exposure in order to hold the shutter open against the bias of the spring urging the shutter to a closed opposition.
Maintaining power to the coil of a linear electric motor for an extended period has its drawbacks due mainly to the resulting generation of heat. If not dissipated, the heat could adversely affect the alignment of the optics, cause image distortion and shorten the life of the motor and other heat sensitive components of the shutter system. A fan, heat sink or heat dissipating fins that normally can solve a heat-generating problem are not appropriate in many applications. For example fans are of little use if the shutter is located in a vacuum environment. In military and space exploration applications weight may be an issue so the use of any additional component such as a heat sink or heat radiating fins is not appropriate. Reference is made to U.S. Ser. No. 11/099,744, as disclosing a shutter assembly that is bi-stable in that it allows the shutter to remain open or closed for long periods without generating excessive heat.
In some applications space also is a limitation. Space limitations particularly in the region of the shutter opening dictate the parameters of size and placement of apparatus for holding the shutter open. For example, components placed near the shutter opening must have a relatively low profile so as not to interfere with the cone angle of the light passing through the open shutter. Space limitations also complicate the substitution of one shutter assembly for another as in changing shutter size while maintaining the same base structure.
As noted above, most prior art shutter assemblies mechanically couple a linear electric motor to the shutter for opening and closing the lens opening. For proper operation, particularly at high speeds, the mechanical linkage must be precisely made and the movement of the linkage must be dampened. To applicant's knowledge elimination of a damper system entirely has not been attempted or if attempted, has not been commercially successful.
Accordingly, it is an object of the present invention to provide an operating system for a rotary shutter that eliminates the need for a mechanical linkage between an actuator and the shutter to open and close the shutter.
Another object of the present invention is to provide is to provide a rotary shutter having an electromagnetic operating system.
A further object of the present invention is to provide a method of operating a rotary shutter utilizing electromagnetic energy for opening and closing the shutter.